A description is given below of a manufacturing method including bonding an optical film to an optical display unit (such as a glass substrate unit in which a liquid crystal is sealed). First, a material roll of a long sheet product including an optical film member is manufactured. For example, the “long sheet product” includes a raw material for a polarizing plate for use in a liquid crystal display. For example, a roll of a raw material for a polarizing plate is manufactured by the process described below. The upstream process includes (A) the step of obtaining a polarizer; (B) the step of manufacturing a polarizing plate, which includes placing a polarizer protecting film on one or both sides of the polarizer with an adhesive interposed therebetween and drying the laminate to give a polarizing plate; and (C) the step of bonding a release film (also called “separator”) and a surface protecting film. In the upstream process, a long sheet product is manufactured, wound into a roll and subjected to the downstream process.
(D) The step of slitting the material roll is then performed, in which since the material roll is wide, the material is slit into a predetermined size depending on the size of an optical display unit (the final product). As mentioned above, the long sheet product is manufactured in the form of a material roll. When the predetermined length is not reached (for example, when the long sheet is partially cut due to a continuous defective state), two or more material rolls are joined to form a single material roll in some cases. Conventional examples of the joining method include the methods shown in FIG. 10, such as methods including layering an end portion of a sheet product 701 and an end portion of another sheet product 702 and bonding them by fusion or with an adhesive tape.
The process may also include continuously feeding the sheet product from the material roll, peeling off only the separator, and automatically inspecting any defect in the polarizing plate. In this case, if the process is stopped for every material roll, the work efficiency will be reduced. Therefore, it is proposed that an end portion of the sheet product being inspected should be joined to an end portion of the next sheet product. However, when the end portions are layered and joined as mentioned above, it is impossible to peel off only the separator.
Alternatively, as shown in FIG. 11, end portions may be joined with an adhesive tape 703 without overlapping. In this case, however, delamination sometimes starts from the pressure-sensitive adhesive on the surface protecting film side, and it is difficult to peel off only the separator with a probability of 100%.
Next, a description is given of the step of bonding an optical member-containing sheet product to a substrate as a component of an optical display unit. For example, Patent Literature 1 (Japanese Patent Application Laid-Open (JP-A) No. 2007-140046) discloses a process including unwinding and feeding a belt-shaped sheet product from a roll of the sheet product, detecting any defect in the sheet product, cutting the sheet product into individual pieces based on the result of the detection, and bonding each cut piece to a substrate, wherein in the bonding, only the separator is peeled off from the sheet product, and then the sheet product is bonded to the substrate with the remaining pressure-sensitive adhesive interposed therebetween.
Alternatively, another proposed method includes cutting members other than the separator, while keeping the separator continuous, and bonding the sheet product to a substrate with the remaining pressure-sensitive adhesive interposed therebetween, while peeling off only the separator. In order to perform the bonding process continuously, the sheet product being supplied needs to be joined to the next sheet product as mentioned above. Also in this case, when end portions are joined without overlapping as mentioned above and shown in FIG. 11, delamination sometimes starts from the pressure-sensitive adhesive on the surface protecting film side. Such a case is not preferred because of low continuous productivity, and it has been demanded to properly peel off only the release film.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2007-140046